1. Field of the Invention
This invention relates to an improved measuring lance to be inserted into a bath of molten metal, for example, molten steel, for measuring the temperature, composition, etc. of the bath.
2. Description of the Prior Art
It has been a common practice to insert a measuring lance of this kind into a molten metal, for example, a molten steel which is being refined in a converter, for retrieving a sample and measuring the composition of the steel.
The measuring lance for such purpose is generally provided with a thermocouple in its receptacle chamber for measuring the carbon content based upon the solidification temperature of the steel. An example of such measuring lance is disclosed in U.S. Pat. No. 3,685,359.
However, it often happens with such a lance that accurate measuring of the temperature of the molten steel cannot be effected for the reasons described below.
For instance, the thermocouples are protected by a tube made of hard glass of 0.5 to 1.0 mm. When it comes into contact with the molten steel, the air inside the glass tube is expanded, whereby the tube is broken, especially in its curved portion, and the air inside the tube escapes into the molten steel just sampled, which results in formation of a pipe.
When a pipe is formed like this, accurate measuring of the solidification temperature of the molten steel by the use of a thermocouple becomes difficult, which results in that accurate measuring of the carbon content in the steel cannot be carried out and in addition Count VAC analysis (analysis by vacuum optical emission spectrometer developed by Applied Research Laboratories Company) cannot be effected accurately for the subsequent measuring of the other components in the steel.
The conventional measuring lance consists often of a deoxidation chamber and a receptacle chamber which are made of shell mold or casting iron. Sometimes the lance has only one chamber which serves as both the deoxidation chamber and the receptacle chamber. This invention involves both arrangements.
In the case where shell mold is used, it absorbes water because it is hygroscopic. When it comes into contact with the molten steel, the water is decomposed to thereby generate bubbles of hydrogen gas which makes it difficult to sample the molten steel. In the case where casting iron is used, a part thereof, particularly a corner part such as a mouth for taking up the molten steel, etc., is melted and entrained in the molten steel, which prevents accurate measuring of the composition of the steel.
Furthermore, the measuring lance has its outer circumference composed generally of refractory or fire-resisting papers and the like. Thus, when the lance is dipped into the molten steel, the refractory papers are naturally heated to emit vapor, tar, etc., whereby the connector to connect lance parts and the lead wires to conduct the generated electromotive force tend to be injured by the vapor or tar, etc. thereby resulting in leakage of the electromotive force and a hindering in the accurate measuring of the molten steel. In addition the tar, dust and the like tends to adhere to the connector thus resulting in an increase of contact resistance and a reading of a value lower than the actual value of the electromotive force. This, of course, prevents the accurate measuring of the molten steel.